A partially purified preparation of chicken pituitary gonadotrophin, thought to be predominantly fsh, was tested for ovarystimulating activity by daily intramuscular injection into hypophysectomized hens.
At the levels used, it did not induce follicle development or steroid release in regressed ovaries 10 to 15 days after pituitary removal. Histological examination of thyroid glands indicated that the fraction lacked tsh. When injections commenced at the time of hypophysectomy, ovarian regression was delayed. Ovary and oviduct weights were maintained, in some cases at levels approaching those of intact laying hens. Some ovulations were induced; the eggs laid during treatment tended to be smaller than normal, with less yolk, albumen and shell. Incorporation of dye in the yolk of developing follicles demonstrated that some yolk deposition took place after pituitary removal, in response to treatment. It was not determined whether the lower weights of eggs laid after hypophysectomy were related to a reduced rate of yolk deposition.
It is suggested that a qualitative difference exists between the hormone requirements for the initiation of follicle development and the maintenance of follicle growth by deposition of yolk. The possible involvement of tsh and of a critical fsh : lh ratio are discussed.